1. Field of the Invention
The present invention relates to a method for the preparation of polydiorganosiloxane having a pendant alkenyl radical in the middle of the molecular chain. More specifically, the present invention relates to a method for the preparation, by nonequilibrium polymerization, of polydiorganosiloxane having an alkenyl radical at least as a pendent radical in the middle of the molecular chain and having freely selected groups at both molecular terminals.
2. Prior Art
Equilibrium polymerization involving the ring-opening polymerization of cyclic trisiloxane under alkali metal catalysis is a procedure known and practiced in the art, such as described by Johannson in U.S. Pat. No. 3,002,951, issued Oct. 3, 1961. Johannson teaches alkali metal polyorganosiloxane salts, such as the compound of the formula ##STR3## can be used to polymerize polydiorganosiloxane cyclic trimers by heating the mixture at temperatures in the range of from 30.degree. C. to 250.degree. C. for 5 minutes to 3 days to produce linear polydiorganosiloxanes. Johannson teaches that with his method that the cyclotrisiloxanes will form high polymers at a rate appreciably greater than the degradation of these high polymers to cyclic siloxanes where these are primarily cyclotetrasiloxanes.
Another method for preparing polymers under nonequilibrium conditions is described in McVannel in U.S. Pat. No. 3,294,740, issued Dec. 27, 1966. McVannel teaches that cyclotrisiloxanes can be polymerized without the need to deactivate the catalyst to stabilize the produced linear polymers. McVannel achieves this by using as the polymerization catalyst alkali metal phenoxides or other phenyl compounds having from one to three MO- groups bonded to the aromatic ring of the formula ##STR4## where R" is a monovalent hydrocarbon radical, a monovalent halogenated hydrocarbon radical, halogen atom, or monovalent hydrocarbonoxy radical, and p is 0 to 3, r is 1 to 3, and M is an alkali metal atom. McVannel teaches that the polymerization temperature can be any temperature including room temperature, but preferably from 50.degree. C. to 200.degree. C. McVannel teaches that traces of water may cause depolymerization and that certain metal oxides can be used to remove the water, such as calcium oxide. McVannel also teaches carrying out the polymerization in an organic solvent.
Razzano in U.S. Pat. No. 4,075,169, issued Feb. 21, 1978, teaches that perfluoroalkylethylene substituted cyclic trisiloxanes can be polymerized to make block copolymers using certain dilithium compounds, such as those of the formulae: ##STR5## where R.sup.3 is hydrogen or a lower alkyl radical of one to eight carbon atoms. Razzano teaches using a solvent promoter at reflux temperatures of 55.degree. C. to 85.degree. C. The block copolymers prepared by Razzano's method are particularly described as containing trifluoropropylmethylsiloxane units and diphenylsiloxane units, but alkylvinylsiloxane units are also suggested.
Bluestein in U.S. Pat. No. 4,287,353 issued Sept. 1, 1981 teaches a method for producing silanol chain-stopped fluorosilicone fluid by reacting at 25.degree. C. to 100.degree. C. cyclic fluorosiloxane trimer, water, a polymerization catalyst such as KOH, and a polyethyleneglycol dimethyl ether promoter. In a more specific method Bluestein teaches using a mixture of fluoro-substituted cyclotrisiloxane and one or more of dimethylsilicone cyclic trimer, methylvinylsilicone cyclic trimer, methylphenylsilicone cyclic trimer, and diphenylsilicone cyclic trimer.
Furthermore, it is also known that nonequilibrium polymerization can be carried out by so-called "living polymerization" using a lithium catalyst. For example, as disclosed in J. Saam, et al., in Macromolecules, Volume 3, Number 1, page 1 (1970), after the ring-opening of hexamethylcyclotrisiloxane using butyllithium, polymerization is terminated by the addition of vinylchlorosilane to afford polydiorganosiloxane having a vinyl group at one terminal. The same method for the preparation of organopolysiloxane is also disclosed in Japanese Patent Application Laid Open [Kokai] Number 59-78236 [78236/84], published May 7, 1984, assigned to Toa Gosei Chem. Ind. Ltd. This method of introducing functional groups through a functionalized polymerization termination agent is generally known as the "termination method."
3. Problems in the Prior Art
However, this prior art suffers from the following problem: in the termination method in living polymerization, the chain-capping reaction at the terminals is conducted when high molecular weights have been reached, and alkenyl thus can be introduced only at the molecular chain terminals. Furthermore, when the introduction of pendant alkenyl into the molecule is attempted by equilibrium polymerization, not only is it not possible to control the position of the alkenyl group, but polydiorganosiloxane completely lacking alkenyl in the molecule is produced as a by-product.